Add a fully functional STM32F1 port, currently mostly targeting STM32F103
microcontrollers. This requires an 8 MHz XTAL. The maximum possible step rate
is around 282K steps per second.
This uses stm32flash to burn the firmware. The bootloader needs to be started
by setting BOOT0 to 1 and resetting the MCU. There is no automatic bootloader,
unlike on Arduino.
Signed-off-by: Grigori Goronzy <greg@kinoho.net>
